The present invention relates to a magnetizing method of a rotor of a motor and, more particularly, to a method of magnetizing a motor in which an integrated type magnet member using no yoke member is used as a rotor.
A conventional permanent magnet rotor consists of divided magnets 2 as many as only the number of poles (four poles) which are arranged around a yoke 1 as shown in FIG. 1. A magnetic path 3 of each magnet 2 is orientated toward the center of the yoke 1 as shown by a broken line. The rotor having such a constitution is disclosed in, for example, JP-A 57-142165 filed in Japan by Hitachi, Ltd. on Feb. 26, 1981.
After each of the magnet 2 split type rotors were individually worked, they are fixedly attached to the outer peripheral portion of the yoke 1. Therefore, there are the following problems. Namely, the magnets 2 need to be uniformly worked and the surfaces of the yoke 1 which are come into contact with the magnets 2 also need to be worked at a high degree of accuracy, respectively. Further, the divided magnets 2 need to be fixedly positioned to the yoke 1 so as not to move therefrom. Therefore, there is a problem such that if such requirements are intended to be satisfied, the mass productivity of the rotors deteriorates. Moreover, in the case of fixing the split type magnets 2 to the yoke 1, there is a problem such that a gap portion d is caused between the magnets 2 due to a variation in assembly accuracy as shown in FIG. 2, so that the magnetic characteristics of the magnets deteriorate and the performance of the motor deteriorates.
To solve the foregoing problems, a constitution in which an integrated magnet of the polar anisotropic dry type using no yoke is used as the rotor has been examined. According to this magnet, magnetic paths 5 shown by broken lines in a rotor 4 are formed in only the magnet as shown in FIG. 3.
In the case of manufacturing a closed type compressor including a motor therein, if the magnetized magnets are preliminarily assembled to the motor, there is a possibility such that the metal particles deposited onto the magnets during the assembly process causes the sintering of the compressor. To avoid this, after the non-magnetized rotor was assembled to the motor in the compressor housing, it is necessary to allow a current to flow through the stator winding and to magnetize the magnet parts of the rotor by the magnetic fields which are induced by the current flowing through the stator winding. This is a serious problem in the apparatus such that the metal particles deposited to the rotor exerts an influence on a load apparatus of the motor.
In the case of magnetizing the integrated non-magnetized magnet rotor of the polar anisotropic dry type by the magnetic fields which are generated from the stator by supplying a current to the stator winding, if the directions of the stator magnetic fields are not coincident with the directions of the magnetic paths of the magnet rotor, the magnetic flux will be weakened in the portions where the magnetic fields and magnetic paths cross each other, so that even if the magnet rotor is magnetized, a desired motor performance cannot be obtained.